Yajima et al U.S. Pat. No. 4,158,687 discloses composite materials that are reinforced with SiC fibers which are produced by imbedding the fibers in, or layering with, a powdery matrix (Si.sub.3 N.sub.4), pressing, and sintering. Organosilicon binders may be used, but the matrix is not reaction bonded.
Reaction bonding is disclosed in U.S. Pat. Nos. 4,285,895 to Mangels et al and 3,819,786 to May. In the Mangels et al patent reaction bonded Si.sub.3 N.sub.4 is densified by heating under nitrogen gas pressure in the presence of a densification aid which is an oxide of Mg, Y, Ce, or Zr. In the May patent silicon nitride articles are made from a dough-like mixture of Si and binder. The articles are heated in nitrogen after hot-milling and the removal of trichloroethylene from the binder at 130.degree. C.
U.S. Pat. No. 3,926,656 to Mangels is concerned with a multiple mixture containing silicon powder. An injection molding composition of Si powder, paraffin wax, zinc stearate, and Fe.sub.2 O.sub.3 is used to form molded parts which are nitrided to form Si.sub.3 N.sub.4 articles.
U.S. Pat. No. 4,004,937 to Masaaki discloses the use of nickel oxide as a sintering aide for silicon nitride. The silicon nitride ceramic material contains at least one of MgO, ZnO, and NiO in addition to at least one of Al.sub.2 O.sub.3, Cr.sub.2 O.sub.3, Y.sub.2 O.sub.3, TiO.sub.2, and Sn0.sub.2. The mixed powders are formed into a green compact and sintered in an inert gas.